Planar displays are popular for portable displays and displays with space limits because they are light and small in size. To date, planar displays in addition to liquid crystal displays (LCD), organic electro-luminescent displays (OLED), plasma display panels (PDP) and so on, as well as a mode of the optical interference display are of interest.
U.S. Pat. No. 5,835,255 discloses an array of display units of visible light that can be used in a planar display. Please refer to FIG. 1, which depicts a cross-sectional view of a display unit in the prior art. Every optical interference display unit 100 comprises two walls, 102 and 104. Posts 106 support these two walls 102 and 104, and a cavity 108 is subsequently formed. The distance between these two walls 102 and 104, that is, the length of the cavity 108, is D. One of the walls 102 and 104 is a hemi-transmissible/hemi-reflective layer with an absorption rate that partially absorbs visible light, and the other is a light reflective layer that is deformable when voltage is applied. When the incident light passes through the wall 102 or 104 and arrives in the cavity 108, in all visible light spectra, only the visible light with the wavelength corresponding to the formula 1.1 can generate a constructive interference and can be emitted, that is,2D=Nλ  (1.1)where N is a natural number.
When the length D of cavity 108 is equal to half of the wavelength times any natural number, a constructive interference is generated and a sharp light wave is emitted. In the meantime, if the observer follows the direction of the incident light, a reflected light with wavelength λ1 can be observed. Therefore, the display unit 100 is “open”.
The first wall 102 is a hemi-transmissible/hemi-reflective electrode that comprises a substrate, an absorption layer, and a dielectric layer. Incident light passing through the first wall 102 is partially absorbed by the absorption layer. The substrate is made from conductive and transparent materials, such as ITO glass or IZO glass. The absorption layer is made from metal, such as aluminum, chromium or silver and so on. The dielectric layer is made from silicon oxide, silicon nitrite or metal oxide. Metal oxide can be obtained by directly oxidizing a portion of the absorption layer. The second wall 104 is a deformable reflective electrode. It shifts up and down by applying a voltage. The second wall 104 is typically made from dielectric materials/conductive transparent materials, or metal/conductive transparent materials.
FIG. 2 depicts a cross-sectional view of a display unit in the prior art after applying a voltage. As illuminated in FIG. 2, while driven by the voltage, the wall 104 is deformed and falls down towards the wall 102 due to the attraction of static electricity. At this time, the distance between wall 102 and 104, that is, the length of the cavity 108 is not exactly zero, but is d, which can be zero. If we use d instead of D in formula 1.1, only the visible light with a wavelength satisfying formula 1.1, which is λ2, can generate a constructive interference, and be reflected by the wall 104, and pass through the wall 102. Because wall 102 has a high light absorption rate for light with wavelength λ2, all the incident light in the visible light spectrum is filtered out and an observer who follows the direction of the incident light cannot observe any reflected light in the visible light spectrum. The display unit 100 is now “closed”.
An array comprising the display unit 100 controlled by voltage operation is sufficient for a single color planar display, but not for a color planar display. A method known to the art is to manufacture a pixel which comprises three display units with different lengths of the cavities. FIG. 3 and FIG. 4 are cross-section views for the color planar displays comprising display unit known to the arts. FIG. 3 illuminates a cross-section view for a prior art multi-layered color planar display. Multi-layered color planar display 200 comprises three layers, display units 202, 204 and 206. An incident light 208 is reflected by display units 202, 204 and 206. The wavelengths of the reflected light are different, for example, they can be red light, green light and blue light. The reasons to have reflected light with three different wavelengths is that the length of the cavities of display units 202, 204 and 206 are different, and also different reflective mirrors are used. One of the disadvantages of a multi-layered color planar display is its poor resolution. Also, as illuminated in FIG. 3, the blue light is less bright than the red light.
FIG. 4 illuminates a cross-section view for a prior at matrix color planar display. Three display units, display units 302, 304 and 306 are formed on a substrate 300. An incident light 308 is reflected by display units 302, 304 and 306. The wavelengths of the reflected light are different, for example, they are red light, green light and blue light. The reason to have reflected light with three different wavelengths is that the lengths of the cavities of display units 302, 304 and 306 are different. It is not required to use different reflective mirrors. The resolution is good, and the brightness of every color light is similar. However, display units with three different lengths of cavities need to be manufactured separately, for example, the region for forming the display units 304 and 306 is shielded by photo-resist while the process for forming the display unit 302 is performed. The manufacturing process is complicated and the yield is low. Moreover, the errors introduced during the manufacturing process, for instance, the errors of the lengths of cavities may cause red shift or blue shift. The mistake is uncorrectable and the substrate is wasted.
Therefore, it is important to develop a color optical interference display plate which has high resolution and brightness and is easy to manufacture.